docs: def extract_asset_tags(dstore, tagname):
      """
      Extract an array of asset tags for the given tagname. Use it as
      /extract/asset_tags or /extract/asset_tags/taxonomy
      """
      tagcol = dstore['assetcol/tagcol']
      if tagname:
          yield tagname, barray(tagcol.gen_tags(tagname))
      for tagname in tagcol.tagnames:
          yield tagname, barray(tagcol.gen_tags(tagname))